Electronic endoscope

ABSTRACT

An electronic endoscope has a tip portion with a tip end. This electronic endoscope comprises an imaging element provided in the tip portion; an imaging optical system provided in the tip portion at a position closer to the tip end than the imaging element; and a plurality of light-emitting elements for emitting light, each of which is provided in the tip portion at a position closer to the tip end than the imaging element. Each of the light-emitting elements is arranged such that a part of the light-emitting element is seen so as to overlap with the imaging element when viewed from the optical axis direction of the imaging optical system. According to this arrangement, it is possible to reduce the diameter of the tip portion of the electronic endoscope. Further, when such an electronic endoscope is used as a medical endoscope, it becomes possible to relieve the pain that patients may feel.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an electronic endoscope.

[0003] 2. Description of the Prior Art

[0004] In the medical field, for example, electronic endoscope systemshave been used as diagnostic systems for examining internal portions(e.g., the alimentary canal) of the human body.

[0005] In general, such electronic endoscope systems include a lightsource device and an electronic endoscope which is removably mounted(connected) to the light source device.

[0006]FIG. 11 is a bottom view and a cross-sectional view of a tipportion of the prior-art electronic endoscope.

[0007] As shown in FIG. 11, the prior-art electronic endoscope 100includes an endoscope main body 110. In a tip portion 120 of theendoscope main body 110, there are provided a CCD imaging sensor(imaging element) 130 and a pair of light-emitting diodes(light-emitting elements) 140 for emitting light toward an observationpart of a patient.

[0008] In this prior-art electronic endoscope 100, these light-emittingdiodes 140 are arranged at the opposite sides of the CCD imaging sensor130 as shown in FIG. 11.

[0009] Further, in front of the CCD imaging sensor 130, there isprovided an imaging optical system that includes an objective lens 150and convex lenses 160 and 170.

[0010] Furthermore, a diverging lens (light distribution lens) 180 isprovided in front of each of the light-emitting diodes 140.

[0011] However, in the prior-art electronic endoscope 100 thelight-emitting diodes 140 are arranged at the opposite sides of the CCDimaging sensor 130, and this results in a problem that the diameter ofthe endoscope main body 110 of the electronic endoscope 100 becomeslarge.

SUMMARY OF THE INVENTION

[0012] Therefore, it is an object of the present invention to provide anelectronic endoscope provided with an endoscope main body that has arelatively small diameter.

[0013] In view of the object, the present invention is directed to anelectronic endoscope having a tip portion with a tip end which is to beinserted into an object to be observed, the electronic endoscopecomprising:

[0014] an imaging element provided in the tip portion;

[0015] an imaging optical system having an optical axis, the imagingoptical system being provided in the tip portion at a position closer tothe tip end than the imaging element; and

[0016] a light-emitting element for emitting light toward an observationpart of the object, the light-emitting element being provided in the tipportion at a position closer to the tip end than the imaging element,wherein the light-emitting element is arranged such that at least a partof the light-emitting element is seen so as to overlap with the imagingelement when viewed from the optical axis direction of the imagingoptical system.

[0017] According to the present invention described above, thelight-emitting element is provided in the tip portion at a positioncloser to the tip end than the imaging element. In addition, thelight-emitting element is arranged such that at least a part of thelight-emitting element is seen so as to overlap with the imaging elementwhen viewed from the optical axis direction of the imaging opticalsystem. As a result of this arrangement, it becomes possible to reducethe diameter of the electronic endoscope, in particular, the diameter ofthe tip portion of the electronic endoscope. Further, when such anelectronic endoscope that has a small diameter is used as a medicalendoscope, it becomes possible to relieve the pain that patients mayfeel during diagnosis.

[0018] In this invention, it is preferred that the imaging element hasan imaging region that includes at least one shading region fordetecting a reference level of optical black, in which thelight-emitting element is arranged so that at least a part of thelight-emitting element is seen so as to overlap with the shading regionof the imaging element when viewed from the optical axis direction ofthe imaging optical system.

[0019] Further, in this invention, it is also preferred that the imagingoptical system includes a light-deflecting member for deflecting lightrays from the observation part of the object In this case, it ispreferred that the imaging element has an imaging region that includesat least one shading region for detecting a reference level of opticalblack, in which the light-emitting element is arranged such that atleast a part of the light-emitting element is situated within the regionof light rays being directed to the shading region of the imagingelement.

[0020] Furthermore, in this invention, it is also preferred that theimaging element has an imaging region that includes an effective imagingregion on which an image is to be formed by light rays that have passedthrough the imaging optical system.

[0021] Moreover, in this invention, it is also preferred that thelight-emitting element includes a light-emitting diode.

[0022] Another aspect of the present invention is directed to anelectronic endoscope having a tip portion with a tip end which is to beinserted into an object to be observed, the electronic endoscopecomprising:

[0023] an imaging element provided in the tip portion;

[0024] an imaging optical system having an optical axis, the imagingoptical system being provided in the tip portion in front of the imagingelement along the optical axis; and

[0025] a light-emitting element for emitting light toward an observationpart of the object, the light-emitting element being provided in the tipportion at a position closer to the tip end than the imaging element,wherein the light-emitting element is arranged such that at least a partof a projected image which could be formed by projecting thelight-emitting element onto a projecting surface perpendicular to theoptical axis of the imaging optical system overlaps with a projectedimage which could be formed by projecting the imaging element onto theprojecting surface perpendicular to the optical axis.

[0026] In this invention, it is preferred that the imaging element hasan imaging region that includes at least one shading region fordetecting a reference level of optical black, in which thelight-emitting element is arranged such that at least a part of aprojected image which could be formed by projecting the light-emittingelement onto the projecting surface perpendicular to the optical axisoverlaps with a projected image which could be formed by projecting theimaging region of the imaging element onto the projecting surfaceperpendicular to the optical axis.

[0027] Further, in this invention, it is also preferred that theelectronic endoscope further comprises a light-deflecting member fordeflecting light rays emitted from the light-emitting element, whereinthe light-deflecting member is provided in front of the light-emittingelement.

[0028] Furthermore, in this invention, it is also preferred that theimaging optical system includes a light-deflecting member for deflectinglight rays from the observation part of the object.

[0029] Moreover, in this invention, it is also preferred that theimaging element has an imaging region that includes an effective imagingregion on which an image is to be formed by light rays that have passedthrough the imaging optical system.

[0030] Still further, in this invention, it is also preferred that thelight-emitting element includes a light-emitting diode.

[0031] Yet another aspect of the present invention is directed to anelectronic endoscope having a tip portion with a tip end which is to beinserted into an object to be observed, the electronic endoscopecomprising:

[0032] an imaging element provided in the tip portion:

[0033] an imaging optical system having an optical axis, the imagingoptical system being provided in the tip portion at a position closer tothe tip end than the imaging element; and

[0034] a plurality of light-emitting elements for emitting light towardan observation part of the object, each of the light-emitting elementsbeing provided in the tip portion at a position closer to the tip endthan the imaging element, wherein each of the light-emitting elements isarranged such that at least a part of the light-emitting element is seenso as to overlap with the imaging element when viewed from the opticalaxis direction of the imaging optical system.

[0035] Yet another aspect of the present invention is directed to anelectronic endoscope having a tip portion which is to be inserted intoan object to be observed, the electronic endoscope comprising:

[0036] an imaging element provided in the tip portion;

[0037] an imaging optical system having an optical axis, the imagingoptical system being provided in the tip portion in front of the imagingelement along the optical axis; and

[0038] a plurality of light-emitting elements for emitting light towardan observation part of the object, each of the light-emitting elementsbeing provided in the tip portion at a position closer to the tip endthan the imaging element, wherein each of the light-emitting elements isarranged such that at least a part of a projected image which could beformed by projecting the light-emitting element onto a projectingsurface perpendicular to the optical axis of the imaging optical systemoverlaps with a projected image which could be formed by projecting theimaging element onto the projecting surface perpendicular to the opticalaxis.

[0039] These and other objects, structures and advantages of the presentinvention will be apparent more clearly when the following detaileddescription of the preferred embodiments is considered taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040]FIG. 1 is a block diagram which shows a first embodiment of anelectronic endoscope according to the present invention and thestructure of a light source device to which the electronic endoscope isconnected;

[0041]FIG. 2 is a block diagram which shows the structure of a signalpre-processor of the electronic endoscope shown in FIG. 1;

[0042]FIG. 3 is a block diagram which shows the structure of a signalprocessing circuit of the light source device shown in FIG. 1;

[0043]FIG. 4 is a bottom view and a cross-sectional view of the tipportion of the electronic endoscope shown in FIG. 1:

[0044]FIG. 5 is a bottom view of the tip portion of the electronicendoscope shown in FIG. 1, in which an endoscope main body, a CCDimaging sensor, an objective lens and light-emitting diodes are shown asbeing viewed from the optical axis direction of an imaging opticalsystem;

[0045]FIG. 6 is a bottom view of a tip portion of the second embodimentof the endoscope according to the present invention;

[0046]FIG. 7 is a bottom view of the tip portion of the endoscope shownin FIG. 6, in which a main body, a CCD imaging sensor, an objective lensand light-emitting diodes are shown as being viewed from the opticalaxis direction;

[0047]FIG. 8 is a cross-sectional view of a third embodiment of theendoscope according to the present invention, in which a tip portion ofthe endoscope is shown;

[0048]FIG. 9 shows a CCD imaging sensor, a light-emitting diode, andfirst and second triangular prisms provided in the endoscope in FIG. 8;

[0049]FIG. 10 is a cross-sectional view of a fourth embodiment of theendoscope according to the present invention, in which a tip portion ofthe endoscope is shown; and

[0050]FIG. 11 is a bottom view and a cross-sectional view of a tipportion of a prior-art electronic endoscope.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0051] A detailed description of the preferred embodiments of anelectronic endoscope according to the present invention will now begiven below with reference to the appended drawings.

[0052]FIG. 1 is a block diagram which shows a first embodiment of anelectronic endoscope according to the present invention and thestructure of a light source device to which the electronic endoscope isconnected. FIG. 2 is a block diagram which shows the structure of asignal pre-processor of the electronic endoscope shown in FIG. 1. FIG. 3is a block diagram which shows the structure of a signal processingcircuit of the light source device shown in FIG. 1. FIG. 4 is a bottomview and a cross-sectional view of the tip portion of the electronicendoscope shown in FIG. 1. FIG. 5 is a bottom view of the tip portion ofthe electronic endoscope shown in FIG. 1, in which an endoscope mainbody, a CCD imaging sensor, an objective lens and light-emitting diodesare shown as being viewed from the optical axis direction of an imagingoptical system.

[0053] Hereinafter, for easier understanding, the right and leftdirections in the cross-sectional view of FIG. 4 will be simply refereedto as an “optical axis direction” of the imaging optical system.Further, the left side in this figure will be referred to as “tip”, andthe right side will be referred to as “base”. Furthermore, an end at theside of the tip of the tip portion of the main body will be referred asa “tip end.”

[0054] As shown in FIG. 1, an electronic endoscope system (endoscopesystem) 300 includes a light source device 8 and an electronic endoscope1 which is removably connected to the light source device 8.(Hereinafter, the electronic endoscope will be simply referred to as an“endoscope.”)

[0055] The endoscope 1 is equipped with a long flexible (elastic)endoscope main body 2. (Hereinafter, the endoscope main body is simplyreferred to as a “main body.”) The main body 2 includes an operationportion 23 provided at the base end portion thereof.

[0056] As shown in FIG. 4, in the central portion of the tip portion 21of the main body 2, there are provided an imaging optical systemincluding an objective lens 33 and convex lenses 34 and 35; and a CCD(Charge Coupled Device) imaging sensor (imaging element) 5 that includesa transparent glass cover 51 having light transmittivity. The objectivelens 33, the convex lenses 34 and 35 and the CCD imaging sensor 5 arearranged in this order from the tip (i.e., the left side in FIG. 4) tothe base (i.e., the right side in FIG. 4). In this structure, theimaging optical system is arranged in front of the CCD imaging sensor 5along the optical axis O. In other words, the imaging optical system isprovided in the tip portion 21 at a position closer to the tip end ofthe tip portion 21 than the CCD imaging sensor 5.

[0057] The objective lens 33 is formed from a concave lens, and has thelargest diameter among the lenses in the imaging optical system.

[0058] As shown in FIGS. 4 and 5, the CCD imaging sensor 5 (from whichlead wires 54 are excluded) has a roughly rectangular parallelepipedshape.

[0059] Further, as shown in FIG. 5, an imaging region 521 of the CCDimaging sensor 5 has a rectangular shape.

[0060] On each of the opposite short sides 53 a and 53 b (i.e., thesides positioned at both ends along the horizontal scanning direction inFIG. 5) of the imaging region 521 of the CCD imaging sensor 5,band-shaped shading regions 522 and 523 (shown by the slanting lines inFIG. 5) for detecting a reference level of optical black are provided,respectively. Each of the shading regions 522 and 523 is normallyreferred to as “optical black (optical black portion).” In thisconnection, the imaging region 521 from which the shading regions 522and 523 are excluded functions as an effective imaging region 524.

[0061] In this embodiment, the shading region 522 has a width that isconstant in the direction of a line parallel to the short side 53 a, andthe shading region 523 has a width that is constant in the direction ofa line parallel to the short side 53 b. Further, the width of theshading region 522 and the width of the shading region 523 are set to beequal to each other.

[0062] Further, as shown in FIGS. 4 and 5, the CCD imaging sensor 5 isarranged such that the optical axis O of the imaging optical systempasses through the center 525 of the effective imaging region 524 of theCCD imaging sensor 5, and that the shading regions 522 and 523 of theimaging region 521 are symmetrically positioned with respect to theoptical axis O.

[0063] Furthermore, as shown in FIG. 4, in the tip portion 21 of themain body 2, there are provided a pair of diverging lenses (lightdistribution lenses) 31 and 32, and a pair of light-emitting diodes(light-emitting elements) 61 and 62. The diverging lenses 31 and 32 arerespectively arranged in front of the corresponding light-emittingdiodes 61 and 62. Namely, each of the diverging lenses 31 and 32 isarranged at the tip side of the corresponding light-emitting diode.

[0064] Each of the diverging lenses 31 and 32 is formed from a convexlens, and has substantially the same diameter as that of thecorresponding light-emitting diode. Specifically, each of thelight-emitting diodes 61 and 62 is arranged so that its center issubstantially aligned with the center of the corresponding diverginglens when viewed from the optical axis direction of the imaging opticalsystem. (Hereinafter, the optical axis direction of the imaging opticalsystem is simply referred to as the “optical axis direction.”)

[0065] In this connection, as for the light-emitting element of thepresent invention, a lamp which generates (emits) light by supplyingelectrical power thereto may be used if it has such shape and size thatcan be housed within the tip portion of the endoscope. However, alight-emitting diode should preferably be used in this invention, sincesuch a light-emitting diode has a small size and it can be used for along period of time with a small amount of electrical power.

[0066] Next, the arrangement of each of light-emitting diodes 61 and 62will be described in more detail.

[0067] As shown in FIG. 4, each of the light-emitting diodes 61 and 62is provided in front of the CCD imaging sensor 5 along the optical axisO. In other words, each of the light-emitting diodes 61 and 62 isprovided in the tip portion 21 at a position closer to the tip end ofthe tip portion 21 than the CCD imaging sensor 5. Further, theselight-emitting diodes 61 and 62 are respectively arranged at oppositesides of the CCD imaging sensor 5 so that the imaging optical system(which includes the objective lens 33 and convex lenses 34 and 35) ispositioned between the light-emitting diodes 61 and 62 when viewed fromthe optical axis direction.

[0068] Specifically, as shown in FIG. 5, each of the light-emittingdiodes 61 and 62 is arranged such that a part of each light emittingdiode 61 (62) is seen so as to overlap with the CCD imaging sensor 5when viewed from the optical axis direction, but not to overlap with theimaging optical system (which includes the objective lens 33 and convexlenses 34 and 35) and the effective imaging region 524 of the CCDimaging sensor 5.

[0069] In other words, in the endoscope of this invention, each of thelight-emitting diodes 61 and 62 is arranged outside light rays that forman image on the effective imaging region 524 of the CCD imaging sensor 5through the imaging optical system Further, each of the light-emittingdiodes 61 and 62 is arranged such that a part of each of thelight-emitting diodes 61 and 62 is seen so as to overlap with the CCDimaging sensor 5 when viewed from the optical axis direction.

[0070] In more details, in this embodiment, the light-emitting diodes 61and 62 are arranged such that a part of the light-emitting diode 61 isseen so as to overlap with the shading region 522 when viewed from theoptical axis direction, and such that a part of the light-emitting diode62 is seen so as to overlap with the shading region 523 when viewed fromthe optical axis direction.

[0071] Further, in this embodiment, the light-emitting diodes 61 and 62are symmetrically positioned with respect to a first center line(straight line) 55 that is orthogonal to the horizontal scanningdirection in the CCD imaging sensor 5 and that passes through the center525 of the effective imaging region 524 of the CCD imaging sensor 5. Inaddition, the light-emitting diodes 61 and 62 are also symmetricallypositioned with respect to a second center line (straight line) 56 thatis in parallel with the horizontal scanning direction in the CCD imagingsensor 5 and that passes through the center 525 of the effective imagingregion 524 of the CCD imaging sensor 5.

[0072] According to the present invention described above, the endoscopeis provided with even number of light-emitting diodes (twolight-emitting diodes in this embodiment), and the light-emitting diodesare symmetrically positioned with respect to each of the first andsecond center lines 55 and 56. By constructing the endoscope in thisway, it becomes possible to illuminate an observation part of an object(e.g., a patient) more uniformly.

[0073] As shown in FIG. 1, one end of a universal cord (cord-shapedcoupling) 25 is connected to the base end portion of the main body 2.

[0074] The other end of the universal cord 25 is provided with aconnecting portion 26 equipped with a connector 27. By means of theconnector 27, the endoscope 1 is removably connected to the light sourcedevice 8 to establish an electrical connection therebetween.

[0075] Further, a signal pre-processor 7 which is electrically connectedto the connector 27 is housed inside the connecting portion 26, and theCCD imaging sensor 5 is electrically connected to the signalpre-processor 7 via signal lines 47 and 48.

[0076] Furthermore, the light-emitting diodes 61 and 62 are electricallyconnected to the connector 27 via the lead wires 41 and 42,respectively.

[0077] As shown in FIG. 2, the signal pre-processor 7 of the endoscope 1includes a sample-hold and color-separation circuit 71, a CCD processingcircuit (clamping circuit) 72, a television timing generator 73, a CCDtiming generator 74 and a buffer 75.

[0078] As shown in FIG. 1, the light source device 8 includes a lamppower source 81, a system control circuit (control means) 85, a lightregulating circuit 86 and a signal processing circuit 9 which are allhoused in a casing not shown in the drawings.

[0079] As shown in FIG. 3, the signal processing circuit 9 of the lightsource device 8 includes a matrix circuit 91, a gamma correction circuit92, an aperture correction circuit 93, an A/D converter 94, a timinggenerator 95, a memory 96, a D/A converter 97, a buffer 98 and a matrixencoder buffer circuit 99.

[0080] Further, a television monitor (display means) 400 for displayingimages at an observation part (e.g., affected part of a patient) isremovably connected to the light source device 8.

[0081] Next, the operation of the electronic endoscope system 300 willbe described with reference to FIGS. 1 to 3.

[0082] As shown in FIG. 1, when the power supply is turned on,electrical power is supplied from the lamp power source 81 to thelight-emitting diodes 61 and 62, and this causes each light-emittingdiode to emit light. The level of voltage generated in the lamp powersource 81 is controlled between a high level and a low level (i.e., zerovolt) by the system control circuit 85 and the light regulating circuit86. In this regard, the control of the lamp power source 81 will bedescribed later in detail.

[0083] The light emitted from each of the light-emitting diodes 61 and62 is first guided into each of the diverging lenses 31 and 32,respectively. In each diverging lens, the light is first converged andthen diverged to illuminate an observation part (i.e., the section ofthe body to be observed) uniformly.

[0084] The reflected light from the observation part is guided throughthe imaging optical system (which includes the objective lens 33 and theconvex lenses 34 and 35) to form an image on the light-receiving surface52 of the CCD imaging sensor 5 (see FIGS. 1, 4 and 5).

[0085] Meanwhile, as shown in FIG. 2, a horizontal synchronizing signal(HS) and a vertical synchronizing signal (VS) are generated in thetelevision timing generator 73 of the signal pre-processor 7 of theendoscope 1, and these horizontal synchronizing signal (HS) and verticalsynchronizing signal (VS) are inputted into both the CCD processingcircuit 72 and the CCD timing generator 74.

[0086] Further, a synchronizing signal (Sync) is generated in thetelevision timing generator 73, and as shown in FIGS. 1 and 3, thissynchronizing signal (Sync) is inputted into both the system controlcircuit 85 and the timing generator 95 of the signal processing circuit9 of the light source device 8.

[0087] As shown in FIG. 2, driving signals for driving the CCD imagingsensor 5 are generated in the CCD timing generator 74 based on thehorizontal synchronizing signal (HS) and the vertical synchronizingsignal (VS) from the television timing generator 73, and these drivingsignals are outputted from the signal pre-processor 7 via the buffer 75.

[0088] Further, a sample hold signal (SHP) is generated in the CCDtiming generator 74, and this sample hold signal (SHP) is inputted intothe sample-hold and color-separation circuit 71.

[0089] As shown in FIG. 1, the driving signals outputted from the signalpre-processor 7 are inputted into the CCD imaging sensor 5 via thesignal line 47, and the CCD imaging sensor 5 is driven based on suchdriving signals. Now, by driving the CCD imaging sensor 5, it becomespossible for the CCD imaging sensor 5 to take images of the observationpart (namely, images formed on the light-receiving surface 52),whereupon CCD signals are outputted from the CCD imaging sensor 5. TheseCCD signals are inputted into the signal pre-processor 7 via the signalline 48.

[0090] As shown in FIG. 2, the sample-hold and color-separation circuit71 of the signal pre-processor 7 separates the CCD signals into the R(red), G (green) and B (blue) color signals, respectively, in accordancewith the sample hold signals (SHP) from the CCD timing generator 74.Then, the R, G and B signals are respectively inputted into the CCDprocessing circuit 72.

[0091] Further, in the CCD timing generator 74, clamping pulse signals(Clamp) are generated in synchronization with the timing that the R, Gand B signals from the pixels of each of the shading regions 522 and 523(shown in FIG. 5) are inputted into the CCD processing circuit 72. Then,the generated clamping pulse signals are respectively inputted into theCCD processing circuit 72.

[0092] The CCD processing circuit 72 carries out one clamping process inone horizontal scanning (i.e., per each horizontal scanning) insynchronization with the clamping pulse signals.

[0093] In each clamping process, the R, G and B signals are respectivelysampled in synchronization with the respective clamping pulse signalsfrom the CCD timing generator 74. Namely, by sampling each of the R, Gand B signals from the pixels of the shading region 522 (523), areference level of optical black can be detected, and this detectedreference level can be held. (Hereinafter, the reference level ofoptical black is simply referred to as a “reference level.”)

[0094] In the present embodiment, the CCD processing circuit 72 includesa capacitor (not shown in the drawings) which is used as a holding meansfor holding the reference level. Further, the capacitor is designed soas to hold the amount of charge (voltage) which corresponds to thereference level. Accordingly, the reference level can be obtained fromthe voltage value of such a capacitor.

[0095] Further, as shown in FIG. 2, in the CCD processing circuit 72,appropriate R, G and B signals can be obtained by subtracting thereference level component from the R, G and B signals from the pixels ofthe effective region 524. Based on such appropriate signals, twocolor-difference signals (R-Y, B-Y) and a luminance signal (Y) aregenerated. In this way, by subtracting the reference level componentfrom the R, G and B signals, it becomes possible, for example, to removeuseless signal components (such as the dark current component and thelike) from such signals, and this makes it possible to obtainappropriate images.

[0096] As shown in FIGS. 2 and 3, the color-difference signal (R-Y), thecolor-difference signal (B-Y) and the luminance signal (Y) are outputtedfrom the CCD processing circuit 72, and then inputted into the matrixcircuit 91 of the signal processing circuit 9 of the light source device8.

[0097] As shown in FIG. 1, the luminance signal (Y) is also inputtedinto the light regulating circuit 86, and it is used for regulating thequantity of light. Namely, a reference voltage (Vref) for regulating thelight is inputted into the light regulating circuit 86 from the systemcontrol circuit 85, and based on this reference voltage (Vref) and theluminance signal (Y), the light regulating circuit 86 generates acontrol signal. Using the generated control signal, the light regulatingcircuit 86 controls the operation of the lamp power source 81. In thisway, the duty cycle, that is, the ratio of the time of high-voltagelevel (during which the voltage level of the lamp power source 81 ishigh) with respect to the time of low- voltage level (during which thevoltage level of the lamp power source 81 is low, that is zero volt) isadjusted, thus making it possible to properly set the quantity of lightemitted from the light-emitting diodes 61 and 62.

[0098] As shown in FIG. 3, in the matrix circuit 91, thecolor-difference signal (R-Y), the color-difference signal (B-Y) and theluminance signal (Y) are converted into R, G and B signals,respectively.

[0099] Next, after undergoing correction by the gamma correction circuit92 and the aperture correction circuit 93, these R, G and B signals areinputted into the A/D converter 94.

[0100] In the A/D converter 94, the R, G and B signals supplied asanalog signals are converted into digital signals.

[0101] These digital R, G and B signals are temporarily written into thememory 96. In this connection, based on data corresponding to thesignals stored in the memory 96, it is possible to carry out, forexample, a freeze process to capture a desired still image.

[0102] Next, the R, G and B signals are read out from the memory 96 andinputted into the D/A converter 97.

[0103] In the D/A converter 97, the R, G and B signals which aresupplied as digital signals are converted into analog signals. Then, theanalog R, G and B signals are inputted into both the buffer 98 and thematrix encoder buffer circuit 99.

[0104] In the matrix encoder buffer circuit 99, a luminance signal (Y),a chroma signal (C) and a composite signal (Composite) are generatedbased on the analog R, G and B signals from the D/A converter 97 and thesynchronizing signal (Sync) from the timing generator 95, and theseluminance signal (Y), chroma signal (C) and composite signal (Composite)are outputted to an output terminal (not shown in the drawings).

[0105] Further, the R, G and B signals from the D/A converter 97 and thesynchronizing signal (Sync) from the timing generator 95 are inputtedinto the television monitor 400 via the buffer 98.

[0106] Then, a color image (electronic image) taken by the CCD imagingsensor 5, namely, a color image in the form of a moving picture isdisplayed on the television monitor 400.

[0107] As described above, according to the endoscope 1 of the presentinvention, each of the light-emitting diodes 61 and 62 is provided inthe tip portion 21 at a position closer to the tip end of the tipportion 21 than the CCD imaging sensor 5. Further, in the tip portion21, each of the light-emitting diodes 61 and 62 is arranged such that apart of the light-emitting diode 61 (62) is seen so as to overlap withthe shading region 522 (523) when viewed from the optical axisdirection. As a result of this arrangement, it becomes possible toreduce the diameter of the main body 2, in particular, the diameter ofthe tip portion 21 of the main body 2.

[0108] Further, when an endoscope that is provided with such a main bodyhaving a small diameter is used as a medical endoscope, it becomespossible to relieve the pain that patients may feel during diagnosis.

[0109] Next, a second embodiment of the endoscope according to thepresent invention will be described.

[0110]FIG. 6 is a bottom view of a tip portion of the second embodimentof the endoscope according to the present invention. FIG. 7 is a bottomview of the tip portion of the endoscope shown in FIG. 6, in which amain body, a CCD imaging sensor, an objective lens and light-emittingdiodes are shown as being viewed from the optical axis direction. Inthis regard, a detailed description of elements and features of thesecond embodiment that are the same as those of the first embodimentwill not be given, and only main points which are different from thefirst embodiment will be described.

[0111] As shown in FIGS. 6 and 7, in the tip portion 21 of the main body2 of the endoscope 1, there are provided four diverging lenses (lightdistribution lenses) 36-39, and four light-emitting diodes(light-emitting elements) 63-66 which can emit white light. Thediverging lenses 36-39 are respectively arranged in front of thecorresponding light-emitting diodes 63-66. Namely, in the same manner asin the first embodiment, each of the diverging lenses 36-39 is arrangedat the tip side of the corresponding light-emitting diode.

[0112] Each of the diverging lenses 36-39 is formed from a convex lens,and has substantially the same diameter as that of the correspondinglight-emitting diode. Specifically, each of the light-emitting diodes63-66 is arranged so that its center is substantially aligned with thecenter of the corresponding diverging lens when viewed from the opticalaxis direction.

[0113] Next, the arrangements of light-emitting diodes 63-66 in thisembodiment will be described in more detail.

[0114] As shown in FIG. 7, each of the light-emitting diodes 63-66 isprovided in the tip portion 21 in front of the CCD imaging sensor 5along the optical axis O (that is, at a position closer to the tip endof the tip portion 21 than the CCD imaging sensor 5). Specifically, inthe tip portion 21, each of the light-emitting diodes 63-66 is arrangedsuch that each light-emitting diode is seen so as to be positioned onthe corresponding corner section of the CCD imaging sensor S when viewedfrom the optical axis direction.

[0115] Further, in this embodiment, the light-emitting diodes 63-66 arearranged so as to satisfy the following positional relationships(i)-(iv) when viewed from the optical axis direction.

[0116] (i) The light-emitting diode 63 is seen so as to lie within thearea of the CCD imaging sensor 5 with a state that a part of thelight-emitting diode 63 overlaps with the shading region 522, but doesnot overlap with both the imaging optical system and the effectiveimaging region 524.

[0117] (ii) The light-emitting diode 64 is seen so as to lie within thearea of the CCD imaging sensor 5 with a state that a part of thelight-emitting diode 64 overlaps with the shading region 523, but doesnot overlap with both the imaging optical system and the effectiveimaging region 524.

[0118] (iii) The light-emitting diode 65 is seen so as to lie within thearea of the CCD imaging sensor 5 with a state that a part of thelight-emitting diode 65 overlaps with the shading region 523, but doesnot overlap with both the imaging optical system and the effectiveimaging region 524.

[0119] (iv) The light-emitting diode 66 is seen so as to lie within thearea of the CCD imaging sensor 5 with a state that a part of thelight-emitting diode 66 overlaps with the shading region 522, but doesnot overlap with both the imaging optical system and the effectiveimaging region 524.

[0120] Furthermore, in this embodiment, each of the light-emittingdiodes 63-66 is arranged outside light rays that form an image on theeffective imaging region 524 of the CCD imaging sensor 5 through theimaging optical system.

[0121] In addition, the light-emitting diodes 63 66 used in thisembodiment are symmetrically positioned with respect to a first centerline (straight lines) 55 that is orthogonal to the horizontal scanningdirection in the CCD imaging sensor 5 and that passes through the center525 of the effective imaging region 524 of the CCD imaging sensor 5.Further, the light-emitting diodes 63-66 are also symmetricallypositioned with respect to a second center line (straight lines) 56 thatis in parallel with the horizontal scanning direction in the CCD imagingsensor 5 and that passes through the center of the effective imagingregion 524 of the CCD imaging sensor 5.

[0122] According to the endoscope 1 described above, it is possible toachieve the same results as those in the first embodiment of theendoscope 1.

[0123] Further, according to such an endoscope, all of thelight-emitting diodes 63-66 are arranged such that each light-emittingdiode is seen so as to overlap with the CCD imaging sensor 5 when viewedfrom the optical axis direction. By arranging the light-emitting diodesin this manner, it becomes possible to provide an endoscope with a mainbody which has smaller diameter than that in the first embodimentdescribed above.

[0124] Next, a third embodiment of the endoscope according to thepresent invention will be described with reference to FIGS. 8 and 9.

[0125]FIG. 8 is a cross-sectional view of the third embodiment of theendoscope according to the present invention, in which a tip portion ofthe endoscope is shown. FIG. 9 shows a CCD imaging sensor, alight-emitting diode, and first and second triangular prisms provided inthe endoscope in FIG. 8.

[0126] Hereinafter, for easier understanding, the left side in FIGS. 8and 9 will be referred to as “tip”, and the right side will be referredto as “base”. Further, an end at the side of the tip of the tip portionof the main body will be referred as a “tip end.” In addition, it is tobe noted that in this embodiment the optical axis is indicated by thedashed line “O” shown in FIG. 8.

[0127] In this regard, a detailed description of elements and featuresof the third embodiment that are the same as those of the firstembodiment will not be given, and only main points which are differentfrom the first embodiment will be described.

[0128] As shown in FIGS. 8 and 9, in the tip portion 21 of the main body2, there are provided a light-emitting diode 61 and a CCD imaging sensor5. The light-emitting diode 61 and the CCD imaging sensor 5 are arrangedin a side-by-side relation ship along the longitudinal direction of themain body 2 (that is, along the left and right directions in FIG. 8).Further, the light-emitting diode 61 is arranged in the tip portion 21at a position closer to the tip end of the tip portion 21 than the CCDimaging sensor 5.

[0129] The CCD imaging sensor 5 and the light-emitting diode 61 aremounted on a circuit board 11 provided in the tip portion 21. Inaddition, various devices such as an IC chip 12 shown in FIG. 8 are alsomounted on the circuit board 11.

[0130] The CCD imaging sensor 5 is mounted on the circuit board 11 sothat a light-receiving surface 52 thereof faces upward in FIG. 8.Further, as shown in FIGS. 8 and 9, at a position where the CCD imagingsensor 5 is mounted, an opening 111 is formed in the circuit board 11.

[0131] The light-emitting diode. 61 is mounted on the circuit board 11so that a light-emitting side thereof faces upward in FIG. 8. Further,as shown in FIGS. 8 and 9, at a position where the light-emitting diode61 is mounted, an opening 112 is formed in the circuit board 11.

[0132] Further, in the tip portion 21 of the main body 2, a lens holder14 is provided at a position closer to the tip end of the tip portion 21than the opening 111 of the circuit board 11. In this lens holder 14, anobjective lens 33 and convex lenses 34 and 35 are mounted.

[0133] At the side of the base portion of the lens holder 14, that is,at a position of the opening 111 in the circuit board 11, there isprovided a first triangular prism (light-deflecting member) 13. On thesurface 131 of this first triangular prism 13, a reflection film 132 isprovided. In this regard, the first triangular prism 13, the objectivelens 33 and the convex lenses 34 and 35 described above constitute animaging optical system in this embodiment.

[0134] In addition, in the tip portion 21 of the main body 2, anotherlens holder 16 is provided at a position closer to the tip end of thetip portion 21 than the opening 112 of the circuit board 11. In thislens holder 16, diverging lenses 151 and 152 are mounted.

[0135] At the side of the base portion of the lens holder 16, that is,at a position of the opening 112 in the circuit board 11, there isprovided a second triangular prism (light-deflecting member) 17. On thesurface 171 of the second triangular prism 17, a reflection film 172 isprovided.

[0136] In this regard, the diverging lens 151 and 152 and the secondtriangular prism 17 described above constitute a lighting optical systemin this embodiment.

[0137] Further, at the tip end of the tip portion 21, there is provideda transparent glass cover 18.

[0138] In this embodiment, each of the first and second triangularprisms 13 and 17 is formed from a rectangular prism.

[0139] In the endoscope 1 having the structure described above, thelight-emitting diode 61 and the CCD imaging sensor 5 are arranged suchthat a projected image 613 (shown by a phantom line in FIGS. 8 and 9)which could be formed by projecting the light-emitting diode 61 onto aprojecting surface 191 which is virtually established perpendicularly tothe optical axis O overlaps with a projected image 57 which could beformed by projecting the CCD imaging sensor 5 onto the projectingsurface 191.

[0140] By arranging each element in the main body 2 in this way, itbecomes possible to reduce the diameter of the main body 2, inparticular, the diameter of the tip portion 21 of the main body 2.

[0141] Next, arrangements of the CCD imaging sensor 5, thelight-emitting diode 61 and the first and second triangular prisms 13and 17 will be described in more detail.

[0142] As shown in FIG. 9, the light-emitting diode 61 and the secondtriangular prism 17 are arranged such that a part of the secondtriangular prism 17 is situated within the region of light rays (shownby dotted lines) being directed to the shading region 522 of the CCDimaging sensor 5. In other words, the light-emitting diode 61 and thesecond triangular prism 17 are arranged such that a part of a projectedimage which could be formed by projecting the light-emitting diode 61(in particular, an effective region of the light-emitting diode 61) ontoa projecting surface 191 which is virtually established perpendicularlyto the optical axis O overlaps with a projected image which could-beformed by projecting the shading region 522 of the CCD imaging sensor 5onto the projecting surface 191.

[0143] According to the arrangements described above, it is possible todispose the CCD imaging sensor 5 at a position closer to the base end ofthe main body 2 as compared with the case where the second triangularprism 17 is arranged such that a part of the second triangular prism 17is situated out of the region of the light rays being directed to theshading region 522 This arrangement allows the lens holder 14 to beprovided in the tip portion 2 at a position closer to the circuit board11. As a result, it becomes possible to reduce the diameter of the mainbody of the-endoscope.

[0144] As shown in FIG. 8, in the endoscope 1 of this embodiment, lightemitted from the light-emitting diode 61 is reflected toward the tip ofthe main body 2 by means of the reflection film 172 of the secondtriangular prism 17. Namely, when the light emitted from thelight-emitting diode 61 passes through the second triangular prism 17,the light is perpendicularly deflected in the second triangular prism17, so that the deflected light is directed toward the tip of the mainbody 2.

[0145] Then, the light that has passed through the second triangularprism 17 is guided into the diverging lenses 151 and 152 in the lensholder 16. In these diverging lenses, the light is first converged andthen diverged to illuminate an observation part (i.e., the section ofthe body to be observed) uniformly.

[0146] The reflected light from the observation part passes through theimaging optical system and the first triangular prism 13. In the firsttriangular prism 13, the light form the imaging optical system isreflected so as to be directed toward the downside in FIG. 8. Namely,when the light form the imaging optical system passes through the firsttriangular prism 13, the light is perpendicularly deflected, so that thedeflected light is directed toward the imaging surface 52 of the CCDimaging sensor 5 and then forms an image on the imaging surface

[0147] According to the endoscope 1 described above, it is possible toachieve the same results as those in the first embodiment of theendoscope.

[0148] In this invention, no particular limitation is imposed upon thenumber of the light-emitting element to be provided in the endoscope.For example, two or more light-emitting elements may be provided in theendoscope of this invention.

[0149] When a plurality of light-emitting elements are provided in theendoscope 1, it is preferred that in the same manner as in the first andsecond embodiments the light-emitting elements are substantiallysymmetrically positioned with respect to the first center line 55 thatis orthogonal to the horizontal scanning direction in the CCD imagingsensor 5 and that passes through the center of the effective imagingregion 524 of the CCD imaging sensor 5, and with respect to the secondcenter line 56 that is in parallel with the horizontal scanningdirection in the CCD imaging sensor 5 and that passes through the centerof the effective imaging region 524 of the CCD imaging sensor 5.

[0150] Next, a fourth embodiment of the endoscope of this invention willbe described with reference to FIG. 10.

[0151]FIG. 10 is a cross-sectional view of the fourth embodiment of theendoscope according to the present invention, in which a tip portion ofthe endoscope is shown.

[0152] Hereinafter, for easier understanding, the left side in FIG. 10will be referred to as “tip”, and the right side will be referred to as“base”. Further, an end at the side of the tip of the tip portion of themain body will be referred as a “tip end.” In addition, it is to benoted that in this embodiment the optical axis is indicated by thedashed line “O” shown in FIG. 10.

[0153] In this regard, a detailed description of elements and featuresof the fourth embodiment that are the same as those of the thirdembodiment described above will not be given, and only main points whichare different from the third embodiment will be described.

[0154] As shown in FIG. 10, the endoscope 1 in this embodiment isprovided with a light-emitting diode 61 mounted in a lens holder 16.This embodiment does not have a triangular prism like the secondtriangular prism 17 in the third embodiment.

[0155] The light-emitting diode 61 is electrically, connected to acircuit board 11 via the lead wires 611 and 612.

[0156] In the endoscope 1 in this embodiment, the light-emitting diode61 and the CCD imaging sensor 5 are arranged such that thelight-emitting diode 61 is seen so as to overlap with the CCD imagingsensor 5 when viewed from the optical axis direction. In other words,the light-emitting diode 61 and the CCD imaging sensor 5 are arrangedsuch that a projected image 613 which could be formed by projecting thelight-emitting diode 613 onto a projecting surface 191 which isvirtually established perpendicularly to the optical axis O overlapswith a projected image 57 which could be formed by projecting the CCDimaging sensor 5 onto the projecting surface 191.

[0157] Preferably, in this embodiment, as shown in FIG. 10 thelight-emitting diode 61 is arranged in the main body 2 such that a partof the light-emitting diode 61 is situated within the region of lightrays being directed to the shading region 522 of the CCD imaging sensor5. Specifically, the light-emitting diode 61 is arranged in the mainbody 2 such that a part of a projected image which could be formed byprojecting the light-emitting diode 61 onto the projecting surface 191perpendicular to the optical axis O overlaps with a projected imagewhich could be formed by projecting the imaging region 522 of the CCDimaging sensor 5 onto the projecting surface 191 perpendicular to theoptical axis O.

[0158] According to the arrangements described above, it becomespossible to reduce the diameter of the main body 2, in particular, thediameter of the tip portion 21 of the main body 2.

[0159] Further, according to the endoscope 1 in this embodiment, it ispossible to achieve the same results as in the third embodiment of theendoscope described above.

[0160] Hereinabove, the endoscope according to the present invention wasdescribed in detail, but the present invention is not limited to theembodiments described above, and it is possible to replace some of theelements with other elements so long as the same functions are achieved.

[0161] For example, in this invention, the main body 2 may be providedwith one or more function channels. Examples of such a function channelinclude a forceps channel (lumen) through which forceps and treatmentinstruments such as medical laser instruments are to be passed; a watersupplying channel; an air supplying channel; and the like.

[0162] Further, in the present invention, each light-emitting element isnot necessarily arranged so as to overlap with the corresponding shadingregion when viewed from the optical axis direction. For example, in thisinvention, each light-emitting element may be arranged such that atleast a part of the light-emitting element is seen so as to overlap withthe imaging element at the side where the shading region is not placedwhen viewed from the optical axis direction, but not to overlap with theeffective imaging region.

[0163] Furthermore, the endoscope of this invention may have one, three,five, or more light-emitting elements. In this regard, the number oflight-emitting elements to be provided in the endoscope should be two ormore, and preferably be two-eight. In these cases, the number oflight-emitting elements should preferably be even number.

[0164] When the number of light-emitting elements to be provided in theendoscope is set in the manner described above, it becomes possible toproduce an endoscope that can illuminate an observation part of anobject more uniformly.

[0165] Further, although in the embodiments described above alight-emitting diode is used as a light-emitting element, thelight-emitting element to be used in the present invention is notlimited to such a diode. Specifically, the endoscope of this inventionmay use, for example, a lamp that radiates heat and emits light whensupplied electrical power thereto.

[0166] Furthermore, no particular limitation is not imposed upon imagingelements to be used in the present invention. For example, variousimaging elements such as a MOS type imaging sensor, a CPD (ChargePriming Device) and the like may be used in the present invention. Inthis case, both a color imaging element and a monochrome imaging elementcan be used.

[0167] Now, it is to be noted that the endoscope of the presentinvention can be also applied to industrial electronic endoscopes inaddition to the electronic endoscopes for medical use.

[0168] As described above, according to the present invention, it ispossible to produce an electronic endoscope provided with a main bodythat has relatively small diameter. Further, when such an electronicendoscope is used as a medical electronic endoscope, it becomes possibleto relieve the pain that patients may feel during diagnosis.

[0169] Finally, it is to be understood that many changes and additionsmay be made to the embodiments described above without departing fromthe scope and spirit of the invention as defined in the appended claims.

[0170] Further, it is also to be understood that the present disclosurerelates to subject matter contained in Japanese Patent Application No.H11-344987 (filed on Dec. 3, 1999) which is expressly incorporatedherein by reference in its entirely.

What is claimed is:
 1. An electronic endoscope having a tip portion witha tip end which is to be inserted into an object to be observed, theelectronic endoscope comprising: an imaging element provided in the tipportion; an imaging optical system having an optical axis, the imagingoptical system being provided in the tip portion at a position closer tothe tip end than the imaging element; and a light-emitting element foremitting light toward an observation part of the object, thelight-emitting element being provided in the tip portion at a positioncloser to the tip end than the imaging element, wherein thelight-emitting element is arranged such that at least a part of thelight-emitting element is seen so as to overlap with the imaging elementwhen viewed from the optical axis direction of the imaging opticalsystem.
 2. The electronic endoscope as claimed in claim 1 , wherein theimaging element has an imaging region that includes at least one shadingregion for detecting a reference level of optical black, in which thelight-emitting element is arranged so that at least a part of thelight-emitting element is seen so as to overlap with the shading regionof the imaging element when viewed from the optical axis direction ofthe imaging optical system.
 3. The electronic endoscope as claimed inclaim 1 , wherein the imaging optical system includes a light-deflectingmember for deflecting light rays from the observation part of theobject.
 4. The electronic endoscope as claimed in claim 3 , wherein theimaging element has an imaging region that includes at least one shadingregion for detecting a reference level of optical black, in which thelight-emitting element is arranged such that at least a part of thelight-emitting element is situated within the region of light rays beingdirected to the shading region of the imaging element.
 5. The electronicendoscope as claimed in claim 1 , wherein the imaging element has animaging region that includes an effective imaging region on which animage is to be formed by light rays that have passed through the imagingoptical system.
 6. The electronic endoscope as claimed in claim 1 ,wherein the light-emitting element includes a light-emitting diode. 7.An electronic endoscope having a tip portion with a tip end which is tobe inserted into an object to be observed, the electronic endoscopecomprising: an imaging element provided in the tip portion; an imagingoptical system having an optical axis, the imaging optical system beingprovided in the tip portion in front of the imaging element along theoptical axis; and a light-emitting element for emitting light toward anobservation part of the object, the light-emitting element beingprovided in the tip portion at a position closer to the tip end than theimaging element, wherein the light-emitting element is arranged suchthat at least a part of a projected image which could be formed byprojecting the light-emitting element onto a projecting surfaceperpendicular to the optical axis of the imaging optical system overlapswith a projected image which could be formed by projecting the imagingelement onto the projecting surface perpendicular to the optical axis.8. The electronic endoscope as claimed in claim 7 , wherein the imagingelement has an imaging region that includes at least one shading regionfor detecting a reference level of optical black, in which thelight-emitting element is arranged such that at least a part of aprojected image which could be formed by projecting the light-emittingelement onto the projecting surface perpendicular to the optical axisoverlaps with a projected image which could be formed by projecting theimaging region of the imaging element onto the projecting surfaceperpendicular to the optical axis.
 9. The electronic endoscope asclaimed in claim 7 , further comprising a light-deflecting member fordeflecting light rays emitted from the light-emitting element, whereinthe light-deflecting member is provided in front of the light-emittingelement.
 10. The electronic endoscope as claimed in claim 7 , whereinthe imaging optical system includes a light-deflecting member fordeflecting light rays from the observation part of the object.
 11. Theelectronic endoscope as claimed in claim 7 , wherein the imaging elementhas an imaging region that includes an effective imaging region on whichan image is to be formed by light rays that have passed through theimaging optical system.
 12. The electronic endoscope as claimed in claim7 , wherein the light-emitting element includes a light-emitting diode.13. An electronic endoscope having a tip portion with a tip end which isto be inserted into an object to be observed, the electronic endoscopecomprising: an imaging element provided in the tip portion; an imagingoptical system having an optical axis, the imaging optical system beingprovided in the tip portion at a position closer to the tip end than theimaging element; and a plurality of light-emitting elements for emittinglight toward an observation part of the object, each of thelight-emitting elements being provided in the tip portion at a positioncloser to the tip end than the imaging element, wherein each of thelight-emitting elements is arranged such that at least a part of thelight-emitting element is seen so as to overlap with the imaging elementwhen viewed from the optical axis direction of the imaging opticalsystem.
 14. The electronic endoscope as claimed in claim 13 , whereinthe imaging element has an imaging region that includes at least oneshading region for detecting a reference level of optical black, inwhich each of the light-emitting elements is arranged so that at least apart of the light-emitting element is seen so as to overlap with theshading region of the imaging element when viewed from the optical axisdirection of the imaging optical system.
 15. The electronic endoscope asclaimed in claim 13 , wherein the imaging optical system includes alight-deflecting member for deflecting light rays from the observationpart of the object.
 16. The electronic endoscope as claimed in claim 13, wherein the imaging element has an imaging region that includes atleast one shading region for detecting a reference level of opticalblack, in which each of the light-emitting elements is arranged suchthat at least a part of the light-emitting element is situated withinthe region of light rays being directed to the shading region of theimaging element.
 17. The electronic endoscope as claimed in claim 13 ,wherein the imaging element has an imaging region that includes aneffective imaging region on which an image is to be formed by light raysthat have passed through the imaging optical system.
 18. The electronicendoscope as claimed in claim 13 , wherein the plurality oflight-emitting elements include even number of light-emitting elements,and the imaging element has an imaging region that includes an effectiveimaging region on which an image is to be formed, in which thelight-emitting elements are substantially symmetrically positioned withrespect to a center line that is orthogonal to horizontal scanningdirection in the imaging element and that passes through the center ofthe effective imaging region of the imaging element.
 19. The electronicendoscope as claimed in claim 13 , wherein the plurality oflight-emitting elements include even number of light-emitting elements,and the imaging element, of the imaging element has an imaging regionthat includes an effective imaging region on which an image is to beformed, in which the light-emitting elements are substantiallysymmetrically positioned with respect to a first center line that isorthogonal to horizontal scanning direction in the imaging element andthat passes through the center of the effective imaging region of theimaging element, and with respect to a second center line that is inparallel with the horizontal scanning direction in the imaging elementand that passes through the center of the effective imaging region ofthe imaging element.
 20. The electronic endoscope as claimed in claim 13, wherein each of the light-emitting elements includes a light-emittingdiode.
 21. An electronic endoscope having a tip portion with a tip endwhich is to be inserted into an object to be observed, the electronicendoscope comprising: an imaging element provided in the tip portion; animaging optical system having an optical axis, the imaging opticalsystem being provided in the tip portion in front of the imaging elementalong the optical axis; and a plurality of light-emitting elements foremitting light toward an observation part of the object, each of thelight-emitting elements being provided in the tip portion at a positioncloser to the tip end than the imaging element, wherein each of thelight-emitting elements is arranged such that at least a part of aprojected image which could be formed by projecting the light-emittingelement onto a projecting surface perpendicular to the optical axis ofthe imaging optical system overlaps with a projected image which couldbe formed by projecting the imaging element onto the projecting surfaceperpendicular to the optical axis.
 22. The electronic endoscope asclaimed in claim 21 , wherein the imaging element has an imaging regionthat includes at least one shading region for detecting a referencelevel of optical black, in which each of the light-emitting elements isarranged such that at least a part of a projected image which could beformed by projecting the light-emitting element onto the projectingsurface perpendicular to the optical axis overlaps with a projectedimage which could be formed by projecting the imaging region of theimaging element onto the projecting surface perpendicular to the opticalaxis.
 23. The electronic endoscope as claimed in claim 21 , furthercomprising a light-deflecting member for deflecting light rays emittedfrom the light-emitting element, wherein the light-deflecting member isprovided in front of the light-emitting element.
 24. The electronicendoscope as claimed in claim 21 , wherein the imaging optical systemincludes a light-deflecting member for deflecting light rays from theobservation part of the object.
 25. The electronic endoscope as claimedin claim 21 , wherein the imaging element has an imaging region thatincludes an effective imaging region on which an image is to be formedby light rays that have passed through the imaging optical system. 26.The electronic endoscope as claimed in claim 21 , wherein the pluralityof light-emitting elements include even number of light-emittingelements, and the imaging element has an imaging region that includes aneffective imaging region on which an image is to be formed, in which thelight-emitting elements are substantially symmetrically positioned withrespect to a center line that is orthogonal to horizontal scanningdirection in the imaging element and that passes through the enter ofthe effective imaging region of the imaging element.
 27. The electronicendoscope as claimed in claim 13 , wherein the plurality oflight-emitting elements include even number of light-emitting elements,and the imaging element of the imaging element has an imaging regionthat includes an effective imaging region on which an image is to beformed, in which the light-emitting elements are substantiallysymmetrically positioned with respect to a first center line that isorthogonal to horizontal scanning direction in the imaging element andthat passes through the center of the effective imaging region of theimaging element, and with respect to a second center line that is inparallel with the horizontal scanning direction in the imaging elementand that passes through the center of the effective imaging region ofthe imaging element.
 28. The electronic endoscope as claimed in claim 21, wherein each of the light-emitting elements includes a light-emittingdiode.